Google on Thursday announced that it would require new Chrome extension developers to pay a one-time $5 registration fee as a way to stymie malicious add-ons for its browser.

The company also launched a preview of its Chrome Web Store, giving developers a chance to experiment with the online mart before it goes public later this year. Developers can use the store to give away or sell their browser extensions, themes and Web apps.

"[The signup fee] is intended to create better safeguards against fraudulent extensions in the gallery and limit the activity of malicious developer accounts," said product manager Gregor Hochmuth in a blog post.

The payment must be made using Google Checkout, which links payments to a credit card, thereby creating a paper trail to the developer -- or at least to the billing address and phone number recorded by the credit card company.

By charging the fee, "Google gets some more information about the human on the other end [of the developer account]," said Andrew Storms, director of security at nCircle Security. "It adds some legitimacy to the developer."

A Chrome rival noted the paper trail aspect of the new registration fee, too. "Someone pointed out the $5 registration fee for Chrome Extension Gallery creates a paper trail, which is a good point," said Mike Beltzner, Mozilla's director of Firefox development, in a Twitter message on Thursday.

Google's new requirement could also act as a tripwire, added Storms: The entry fee is low enough for most legitimate developers to hurdle, but it's high enough that it would be a burden for hackers who would be forced to create multiple new accounts to replace those that are sniffed out and disabled when users report malicious add-ons.

Developers who have already created and uploaded a Chrome extension or theme are grandfathered in and won't have to pony up the payment, Hochmuth said.

On the plus side, Chrome extension developers will be able to charge for their wares when the Chrome Web Store opens for business later this year.

Google has set the minimum price for an add-on, theme or Web app at $1.99 -- though developers can continue to give away their work if they want -- and it will take a 5% cut of the purchase price, along with a 30-cent transaction fee for each download and payment. So a developer who charges the minimum $1.99 for an extension would receive $1.59 per download.

Developers can charge a one-time fee or sell their software via monthly or annual subscriptions.

Google isn't the first open-source browser vendor to let developers make money on their add-ons.

In July 2009, Mozilla kicked off a program that let Firefox add-on developers place a "Contribute" button in the install process. Users who clicked on the button pitched in with money drawn from their PayPal accounts. Mozilla does not take a piece of the action, and it lets the developers decide how much, if anything, to ask users to pay.

According to data published last January by Mozilla, developers received more than $42,000 in contributions during the program's first four months of operation.